According to an article that just appeared in Science magazine, scientists in Germany have completed building a stellarator by the name of Wendelstein 7-X (W7-X), and are seeking regulatory permission to turn the facility on in November. If you can’t get past the Science paywall, here’s an article in the popular media with some links. Like the much bigger ITER facility now under construction at Cadarache in France, W7-X is a magnetic fusion device. In other words, its goal is to confine a plasma of heavy hydrogen isotopes at temperatures much hotter than the center of the sun with powerful magnetic fields in order to get them to fuse, releasing energy in the process. There are significant differences between stellarators and the tokamak design used for ITER, but in both approaches the idea is to hold the plasma in place long enough to get significantly more fusion energy out than was necessary to confine and heat the plasma. Both approaches are probably scientifically feasible. Both are also white elephants, and a waste of scarce research dollars.
The problem is that both designs have an Achilles heel. Its name is tritium. Tritium is a heavy isotope of hydrogen with a nucleus containing a proton and two neutrons instead of the usual lone proton. Fusion reactions between tritium and deuterium, another heavy isotope of hydrogen with a single neutron in addition to the usual proton, begin to occur fast enough to be attractive as an energy source at plasma temperatures and densities much less than would be necessary for any alternative reaction. The deuterium-tritium, or DT, reaction will remain the only feasible one for both stellarator and tokamak fusion reactors for the foreseeable future. Unfortunately, tritium occurs in nature in only tiny trace amounts.
The question is, then, where do you get the tritium fuel to keep the fusion reactions going? Well, in addition to a helium nucleus, the DT fusion reaction produces a fast neutron. These can react with lithium to produce tritium. If a lithium-containing blanket could be built surrounding the reaction chamber in such a way as to avoid interfering with the magnetic fields, and yet thick enough and close enough to capture enough of the neutrons, then it should be possible to generate enough tritium to replace that burned up in the fusion process. It sounds complicated but, again, it appears to be at least scientifically feasible. However, it is by no means as certain that it is economically feasible.
Consider what we’re dealing with here. Tritium is an extremely slippery material that can pass right through walls of some types of metal. It is also highly radioactive, with a half-life of about 12.3 years. It will be necessary to find some way to efficiently extract it from the lithium blanket, allowing none of it to leak into the surrounding environment. If any of it gets away, it will be easily detectable. The neighbors are sure to complain and, probably, lawyer up. Again, all this might be doable. The problem is that it will never be doable at a low enough cost to make fusion reactor designs based on these approaches even remotely economically competitive with the non-fossil alternative sources of energy that will be available for, at the very least, the next several centuries.
What’s that? Reactor design studies by large and prestigious universities and corporations have all come to the conclusion that these magnetic fusion beasts will be able to produce electricity at least as cheaply as the competition? I don’t think so. I’ve participated in just such a government-funded study, conducted by a major corporation as prime contractor, with several other prominent universities and corporations participating as subcontractors. I’m familiar with the methodology used in several others. In general, it’s possible to make the cost electricity come out at whatever figure you choose, within reason, using the most approved methods and the most sound project management and financial software. If the government is funding the work, it can be safely assumed that they don’t want to hear something like, “Fuggedaboudit, this thing will be way too expensive to build and run.” That would make the office that funded the work look silly, and the fusion researchers involved in the design look like welfare queens in white coats. The “right” cost numbers will always come out of these studies in the end.
I submit that a better way to come up with a cost estimate is to use a little common sense. Do you really think that a commercial power company will be able to master the intricacies of tritium production and extraction from the vicinity of a highly radioactive reaction chamber at anywhere near the cost of, say, wind and solar combined with next generation nuclear reactors for baseload power? If you do, you’re a great deal more optimistic than me. W7-X cost a billion euros. ITER is slated to cost 13 billion, and will likely come in at well over that. With research money hard to come by in Europe for much worthier projects, throwing amounts like that down a rat hole doesn’t seem like a good plan.
All this may come as a disappointment to fusion enthusiasts. On the other hand, you may want to consider the fact that, if fusion had been easy, we would probably have managed to blow ourselves up with pure fusion weapons by now. Beyond that, you never know when some obscure genius might succeed in pulling a rabbit out of their hat in the form of some novel confinement scheme. Several companies claim they have sure-fire approaches that are so good they will be able to dispense with tritium entirely in favor of more plentiful, naturally occurring isotopes. See, for example, here, here, and here, and the summary at the Next Big Future website. I’m not optimistic about any of them, either, but you never know.